docs: Update RelativeLayout.LayoutParams JavaDoc comments

Added changes to make purpose/usage of RelativeLayout.LayoutParams more
clear:

- clarify the attributes are set on a view contained in a relative layout
- clarify that relative layout uses these values to position the view
- add note that these values are ignored if view is not contained in a
relative layout
- cross-link code sample in Relative Layout guide
- cross-link guide Layout guide to clarify layout params vs regular
attributes

Test: docs change only. Tested with a docs test build.
Change-Id: I4fe1088594c998cee4ff0b2f6295579956c19d6f